Turbine bucket retaining means



Dec. 26, 1961 A. w. RANKIN ETAL 3,

TURBINE BUCKET RETAINING MEANS Filed Feb. 3. 1960 [n ven fors Andrew W Fan/rim Char/es H. Ernesf Jr by 6. @j"

The/r Aifo rney v United States Patent Ofifice 3,014,695 Patented Dec. 26, 1961 3,014,695 TURBINE BUCKET RETAINING MEANS Andrew W. Rankin, Schenectady, and Charles R. Ernest,

Jr., Esperance, N.Y., assignors to General Electric Company, a corporation of New York Filed Feb. 3, 1960, Ser. No. 6,415 Claims. (Cl. 25377) This invention relates to an improved retaining means for an elastic fluid turbine bucket. More particularly, it relates to an improved multiple finger lightweight bucket base providing, for ease of assembly, especially for buckets designed withintegral interfitting cover pieces.

The high rotational speeds of turbine rotors having circumferential rows of buckets attached to the rim of the tangentially, radially, or axially with respect to the rotor axis. I Assembly is complicated where the bucket has an integral cover piece which cooperates with cover pieces of adjacent buckets to form a-shroud around the periphery of thebucket tips. Added strength and reduction of leakage are obtained when the bucket covers follow the contour of the top of the airfoil-shaped buckets, covering the bucket tips completely so that the vane edges do not overhang. Since such bucket covers nest circumferentially about the rim, interference between covers thus results, when the buckets are axially inserted. One solution has required the troublesome expedient of using a jig to hold the entire group of buckets in position for axial insertion simultaneously.

Other arrangements which avoid interference, of the bucket covers are through the use of radially inserted buckets which are held in place by axially inserted pins.

With this manner of retaining the bucket, the load is carried by the pin in shear and very careful machining is required to exactly mate the opposing semi-circles in the rim and bucket base which mate to form a hole for the pin. An example'of a radially inserted bucket is shown Serial No. 626,417, filed on December 5, 1956, now Patent No. 2,974,924 and assigned to the assignee of the 7 present application.

Although tangentially inserted buckets would obviate the cover piece interference problem, the Weight of the bucket-base in relation to the total bucket weight can become inordinately large and a substantial portion of the centrifugal load is caused by the bucket base itself.

This is because either the bucket base or the rim must be enlarged in an axial direction in order to carry the load. As an example, when designing tangentially inserted buckets for high speed, high temperatureapplication, it is not uncommon to have a bucket where the vane load represents only 30% of the total centrifugal load on and the bucket base.

Further reductions in the Weight of the bucket base, with improved stress distribution, may be had by subdividing the base into a number of fingers which are individually attached to the bucket rim. Reference to Patent No. 2,790,620 to A. W. Rankin, issued on April 30, 1957 and assigned to the assignee of the present application, will illustrate such a multiple finger bucket base.

Accordingly, one object of the present invention is to provide an improved bucket retaining means which allows ease of assembly for buckets having integral cover pieces.

in the copending application of Andrew W. Rankin et al.,

the bucket, the remainder being caused by the shroud Another object is to provide an axial-entry turbine bucket which is retained by a pin without requiring extreme accuracy during manufacture of the bucket.

Still another object is to provide an improved arrangement for a pin-retaining means in an axial-entry bucket of the multiple finger type construction.

A further object is to provide an improved bucket having a nested construction so that the vane edges do not overhang the base.

Another object is to provide an improved construction for buckets having multiple finger bases and having contoured integral cover pieces which are subject to interference of the cover pieces when the buckets are individually axially inserted.

The subject matter of the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best .be understood by'reference to the following description taken in connection with the accompanying drawing in which:

FIG. 1 is an end view of two turbine buckets and a portion of the turbine wheel rim showing the method of attachment to the rim; I

PEG. 2 is a perspective view of a single turbine bucket;

FIG. 3 is a developed plan view illustrating the buckets of FIG. 1 during assembly to the rim; and

FIG 4 is an enlarged detail of the pin retaining means and portions of the associated structures.

Generally stated, the invention isv practiced by providing a bucket with-an integral cover piece and a multiple finger base portion. Each of the fingers has a shank portion with a circumferentially enlarged end portion. Complementary radially extending teeth on the rotor rim havesimilar shank portions and enlarged end portions. The bucket shanks define grooves with the tooth shanks to receive pin retaining means therebetwee n. Substantial radial clearances are furnished to allow radial movement of the bucket on the rim whenthe pins are not in place, in order to allow for axial assembly without interference of the bucket covers.

Referring now to FIG. 1 of the drawing, turbine buckets 1t), 11 and a portion of a third bucket 12 are disposed on the rim 13 of a turbi ne wheel. Buckets 10, 11 and 12 are each illustrated in a different radial position on rim 13 in order to illustrate the method of assembly, as explained later. Taking bucket lil as representative of the others, it is comprised of an integral cover. piece 14, a vane portion 15, and a base portion 16 The base portion 16 comprises a platform 17 which acts as an inner wall to prevent the escape of the elastic fiuid fromthe flow path. and multiple fingers 18. The fingers 18, in turn, comprise shank portions 18a and enlarged end'portions 1817. Multiple fingers 18 also. define "axially directed grooves at the intersection of shanks 1811 with the ends 1311..

Referring to the perspective viewof bucket. 10, as shown inFIG. 2, the cover piece-14 is shown to generally follow the contour of the vane portion 15 so'that it defines a circumferentially extending -nose. 14a and a corresponding recess 14b to receive the nose of the next cover piece. Circumferentially extending lips 14c, 14d extend into the region of the adjacent bucket and would ordinarily cause interference with the nose of the adjacent bucket cover piece if the buckets were axially inserted one-by-one. One of the extending lips 14d defines a special axially extending recess 142 to aid in assembly as explained hereinafter.

The platform 17 shown in FIG. 2 has a recess 17a and a corresponding ,circumferentially' extending tab 17b. Tab 1711 on one bucket nests in recess 17a of an adja- 3 cent bucket, with fingers 18 of their respective platform portions aligned, as shown in FIG. 3.

Moving again to FIG 1 of the drawing, the rim of the rotor wheel is provided with axially directed dovetail slots 19 separated by teeth 20. Teeth 20 are shaped similarly to the bucket fingers 18 in that they comprise shank portions 20a and circumferentially enlarged end portions 20b. Rotor teeth 20 also define axially extending grooves 200 at the intersection of portions 20a, 20b. It will be noted that the gap A between adjacent rotor tooth end portions 20b is slightly greater than the circumferential width of the bucket shanks 18a but is less than the circumferential width of the bucket finger end portions 18b. Thus the buckets cannot be radially inserted or removed, but must be inserted axially in rotor grooves 19.

The shape of the axially extending grooves 18c, 260 in the bucket fingers and the rotor teeth respectively, is to be particularly noted- This can be seen most clearly in the enlarged detail view of FIG. 4 showing that rotor tooth groove 20c comprises a portion of a cylindrical Wall 21 and a flat wall 22a, the latter formed on a lip" 22. Similarly, bucket finger groove 180 comprises a cylindrical wall portion 23 and a flat wall portion 24a formed on lip 24. It will be apparent that the opposed surfaces 22a, 24a of the lips 22, 24 are substantially parallel to one another, and that the radial dot-dash line from the turbine wheel axis is substantially normal to these opposed surfaces.

Referring again to FIG. 1 of the drawing, bucket 12 illustrates that pins, one of which is seen at25, are used in order to maintain the buckets in the proper radial position and in order to transmit the force between the bucket fingers 18 and the rotor teeth 20. Pin 25 is shown more clearly in its operating position between mating grooves 180, 200 in FIG. 4. There it will be apparent that pin 25 restrains either inward or outward radial movement of the bucket on rim 13. "Inward radial movement is prevented by the protruding lips 26, 27 of cylindrical walls 21, 23 respectively. Radial movement of the bucket outward under centrifugal force is prevented by the pin 25, which is subjected to a compressive force 'between lip portions 22, 24 at the pointsindicated by arrows 28, 29. i

This configuration differs from previous. pin-retaining bucket constructions in two important respects. First, the pin 25 carries its load in compression where it would normally be much stronger, as opposed to carrying the load in shear between points 28, 29 as with other prior constructions. Secondly, the stress distributions in the rotor teeth ends 2% and the bucket finger ends 18b are greatly improved by the reinforcing elfect of the extending lips 22, 24, which increase the mass of material directly adjacent the load points 28, 29.

The construction shown illustrates pins 25 as being conveniently of circular cross-section, but by suitably modifying design, they could be of other suitable crosssections, e. g. square or triangular.

A generous radial clearance space 30 is provided between the end portions 18b of the bucket fingers and -the bottom of dovetail slot 19. Similarly, a similar generous clearance space 31 is provided between the enlarged end portions 20b of the rotor teeth and bucket platform 17. As will be obvious from FIG. 1, clearance spaces 30, 31 permit bucket 11 to be inserted axially and then moved to a radially inward position and adjacent bucket to be removed to a radially outward position (when pins 25 are not in place). The difference in radial height of the buckets 10, 11 when they are so placed allows the lower surface of nose 14a of bucket 10 to just clear the cover lip 14d on an adjacent bucket by virtue of the special recess 14c formed in lip 14d.

- The plan view of FIG. 3 also illustrates nose 14a with re- 7 spectto the special groove Me.

The method of assembly and operation of the improved turbine bucket will now be described. The radial clearance spaces 30, 31 together with the special groove 14a in the bucket covers allows the blades to be inserted singly onto turbine rim 13 without the requirement of a jig for simultaneous insertion. The assembly proceeds bucket-by-bucket cireumferentially around the rim in the following manner. A bucket, shown as bucket 12, has previously been put in place in its operating position with pin 25 holding the bucket at the proper radial location. Adjacent bucket 11 has already been inserted axially into slots 19 but without placing pins 25.

In order to insert bucket 10, bucket 11 is displaced to its radially innermost position as shown by FIG. 1. Bucket 16 is now inserted axially, with the bucket in its radially outermost position, as shown in FIG. 1, the nose 14a of bucket 10 just clearing the lip 14d of bucket 11 as the bucket is slid axially into place. FIG. 3 shows how this appears in plan view. It will be noted that the tab 17b of the platform of bucket 11 nests in recess 17a of bucket 10 to form a complete platform surface, as the two buckets are slid together.

After bucket 10 has been slid all the way axially into place, nose 14a is nested in recess 14b of the adjacent bucket and the two buckets can move radially with respect to one another. Bucket 11 is now moved radially outward to its operating position, shown by phantom lines 32, and the retaining pins 25 are inserted. Bucket 10 is now moved from its radially outermost position to its radially innermost position, and the next bucket to the left is assembled in the same manner as bucket 10, this bucket (not shown) being inserted axially in its radi' ally outermost position. Thus the buckets are shifted radially inward and outward as the assembly proceeds bucket-by-bucket.

By minor modifications in the construction of the first and last buckets to be assembled, which modifications would be apparent to those skilled in the art, the complete row can be assembled. For instance, the tab 17b on the last bucket, together with the leg 18 under it and that portion of the vane and cover over it, can be machined off so that this last bucket can be assembled without interference. The portion to be machined off on the last bucket is shown by the dashed line 36 in FIG. 3, this being only one method of avoiding intereference in the closing bucket.

The ability to remove and to insert buckets one at a time, simply by removing the pins in adjacent buckets, is an important advantage for replacement of a bucket in the field, where a special jig for simultaneous insertion of all the buckets would ordinarily not be available. Yet the construction allows the use of a curved interlocking and nesting integral bucket cover, which provides good sealing and added strength by avoiding overhanging vane edges.

The invention, however, is not to be construed as being limited to turbine buckets having nesting integral covers, since straight-edge covers could also be employed, while still making use of the improved retaining pin construction illustrated in FIG. 4. With this construction, improved stress distribution in the rotor teeth and the bucket fingers are provided by the extending lips 22, 24. By increasing the surface of the area being loaded with a concentrated load, the allowable stress may be raised due to the improved stress distribution, and. reinforcing effect of the lips 22, 24.

The foregoing construction also reduces the required accuracy of machining the mating grooves 18c, 20c, since they need not perfectly conform to the pin 25. It will With the arrangement shown, however, the extent of relative movement. between grooves 18c, 200 is governed by corners 26, 27 and permissible relative movement with the samediameter pin and the same diameter hole is increased, due to the fact that corners'26, 27 are offset from the radial line.

Thus it will beseen that our improved multiple finger bucket retaining means provides a lightweight bucket which can be axially inserted without the problem of interfering bucket shrouds." This permits the use of nested bucket covers, which reduce leakage and add to the strength of the shroud.

The construction is :also applicable to buckets with axially directed cover pieces or buckets with separately attached shrouds. Since these buckets can be axially inserted without difiiculty, there is no necessity for the radial clearance spaces 30, 31 indicated in FIG. 1.

The combination of the enlarged end portions of the bucket fingers with the disposition of the complementary grooves for the dowel pins results in improved stress distribution in both the bucket fingers and the rotor teeth. In addition, less accuracy is needed in the machining of these grooves. Since a substantial number of buckets are required on a turbine, the elimination of the need for detailed attention to tolerances in these grooves represents a substantial manufacturing saving.

These and many other advantages will be apparent to those skilled in the art, and while there has been de-- scribed what is at present considered to be the preferred embodiment of the invention, it will be understood that still other modifications may be made and it is intended to cover in the appended claims all such modifications as fall Within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A turbo-machine bucket whee-l comprising a circumferential row of buckets disposed on a rotor wheel rim portion, said rim portion defining circumferentially spaced axially extending slots separated by radial rotor teeth having tooth shank portions and circumferentially enlarged tooth end portions and defining axially directed tooth grooves at the intersection of the tooth shank portions and tooth end portions, a plurality of buckets having base portions comprising at least two circumferentially spaced radially extending base fingers disposed in said rim slots, said base fingers comprising finger shank portions and circumferentially enlarged finger end portions and defining axially directed finger grooves at the intersection of the finger shank and finger end portions disposed vis-a-vis said tooth grooves, said tooth grooves and finger grooves each terminating in a flat surface substantially normal to a radial line and radially spaced on the tooth and finger enlarged end portions respectively, and a plurality of retaining pin means disposed in said finger and tooth grooves, whereby the respective enlarged end portions of the bucket fingers and the rotor teeth cooperate with the retaining pin means to prevent the radial disenportion, said n'm portion defining circumferentially spaced.

axially extending slots separated by radial rotor teeth having tooth shank portions and circumferentially enlarged tooth end portions and defining axially directed tooth grooves commencing with a cylindrical portion formed in the tooth shank and terminating in a fiat portion substantially normal to a radial line and forming the radially innermost part of the enlarged tooth end portion, a plurality of buckets having base portions comprising at least two circumferentially spaced radially extending base fingers disposed in said rim slots, said basefingers comprising finger shank portions of a circumferential thickness slightly less than the space between two rotor tooth end portions and circumferentially enlarged finger end portions of a circumferential thickness slightly less than the space-between two rotor tooth shank portions and defining axially directed finger grooves commencing with a cylindrical portion formed in the fin'ger shank and terminating in a fiat surface substantially normal to a radial line and forming the radially outermost part of the finger end portion, said finger and tooth grooves being disposed opposite one another so that said cylindrical portions thereof are substantially concentric, and a plurality of cylindrical retaining pins disposed in the finger and tooth grooves forming close clearances therewith, whereby the flat portions of the finger grooves and tooth grooves increase the surface areas of the enlarged end portions adjacent the retaining pin loading point in order to improve stress distribution.

3. A turbo-machine bucket wheel comprising a circumferential row of buckets disposed on a rotor wheel rim portion, said rim portion defining circumferentially spaced axially extending slots separated by radial rotor teeth having tooth shank portions and circumferentially enlarged tooth end portions and defining axially extending tooth grooves at the intersections of'the tooth shank portions and tooth end portions, a plurality of buckets having base portions comprising at least two circumferentially spaced radially extending base fingers disposed in said rim slots, said base fingers comprising finger shank portions and circumferentially enlarged finger end portions and defining axially directed finger grooves at the intersection of the finger shank and finger end portions disposed vis-a-vis said tooth grooves, said buckets also including integral cover pieces arranged to cooperate with the cover pieces of adjacent buckets to form a substantially continuous shroud member, the radial length of said finger and tooth shank portions being greater than the radial length of said finger and tooth end portions by an amount at least equal to the radial thickness of the integral cover at the point where it engages the cover of an adjacent bucket, whereby adjacent buckets may be displaced radially inward and radially outward respectively to prevent interference of the cover pieces when the buckets are singly inserted, and a plurality of retaining pins disposed in said finger and tooth grooves to prevent radial disengagement of the buckets from the rim.

4. A turbo-machine bucket wheel comprising a circumferential row of turbine buckets disposed on a rotor wheel rim portion, said rim portion defining circumferentially spaced axially extending slots separated by radial rotor teeth having tooth shank portions and circumferentially enlarged tooth end portions and defining axially directed tooth grooves at the intersection of the tooth shankportions and tooth end portions, a plurality of buckets having base portions comprising at least two circumferentially spaced radially extending base fingers disposed in said rim slots, said base fingers comprising finger shank portions having a circumferential dimension slightly less than the gap between said rotor tooth end portions, and circumferentially enlarged finger end'portions having a circumferential dimension slightly less than the gap between said rotor tooth shank portions and defining axially directed finger grooves at the intersection of the finger shank and finger end portions disposed vis-a-vis said tooth grooves, said buckets each including an integral cover nesting in a circumferential direction with adjacent covers, whereby portions of the bucket covers interfere with individual axial insertion of the bucket fingers in the rotor grooves when the buckets are at an equal radial height, said tooth and finger shank portions being radially longer than the tooth and finger end portions by an amount at least equal to the radial thickness of the bucket cover interfering portions, whereby adjacent buckets may be displaced radially inward and radially outward respectively to allow the blades to be individually axially inserted, and a plurality of retaining pin means disposed in said finger and tooth grooves and holding the buckets at equal'radial heights on the rotor wheel, whereby the bucket cover pieces will nest circumferentially and the enlarged end portions of the bucket fingers and the rotor teeth cooperate with the retaining pin means to prevent the radial disengagement of the buckets from the rotor rim portion.

5. The combination accordingto claim 4 where the tooth grooves commence with cylindrical walls cut in the tooth shanks and terminate in flat walls forming the radially innermost parts of the enlarged tooth end portions, and where the finger grooves commence with cylindrical walls cut in the finger shanks and terminate in fiat walls forming the radially outermost part of the en larged finger end portions, and where the retaining pin means constitutes cylindrical dowel pins communicating the centrifugal load between the finger and tooth end portions, whereby the flat walls improve the stress distribution of the pin loading.

UNITED STATES PATENTS Wait June 14, Guy July 20, Rice Dec. 27, Rydmark Apr. 20, Prescott Nov. 4, Sturgess Aug. 5, Persson Sept. 4, Hardigg Jan. 26, Brown Feb. 3,

FOREIGN PATENTS Great Britain Mar. 28, Germany June 11, 

